This invention relates to devices which extract energy from wave action in a body of water. More particularly it concerns the extraction of energy from wave action utilizing a float, a piston-cylinder pump, and an anchor.
Various types of devices which attempt to extract energy from wave action in a body of water or from the wind have been known for some time. For example, U.S. Pat. No. 4,421,461 issued to Hicks et al. discloses a water wave-powered piston pump. The piston pump is mounted on a cradle. The cradle consists of two plates, an upper plate and lower plate. The upper side of the upper plate is secured through a sacrificial link to the float on the upper side and the lower side of the upper plate is secured via a yoke to the pump piston rod which extends out the bottom of the cylinder. The upper side of the lower plate of the cradle is attached to the bottom of the pump cylinder and the lower side of the lower plate is attached to the anchor via a flexible tether. A multiplicity of circumferentially spaced elastomeric springs surround the cylinder of the pump externally to the cylinder. The springs are connected between the upper plate and lower plate of the cradle. A polymeric ball is supported in the upper face of the piston and retained therein by a compression spring biased lock plate. As the float rises the compression spring inside the pump cylinder is compressed which compresses the polymeric ball between the spring biased lock plate and the piston. The polymeric ball expands radially due to the compression and seals the cylinder against leakage past the piston. Also, as the pump rises the multiplicity of circumferentially spaced elastomeric springs external to the cylinder are stretched and are used as external return springs which impel the pump piston rod on its down or refill stroke as the float falls on a wave.
U.S. Pat. No. 4,398,095 issued to Ono discloses a wave-activated power generation system of the float type. A piston-cylinder type pump is anchored to the bottom of a body of water and the float is connected to the piston. As the float rises on a wave the piston is lifted and water is discharged from the pump into an elevated reservoir. Ono uses the hydraulic differential pressure between the air at the surface of the body of water and the depth of the piston cylinder pump in the body of water to move the piston downwardly in the cylinder as the float falls with a descending wave. Because of this use of hydraulic pressure rather than resilient tension between the float and the anchor the Ono device is solidly supported from the bottom of the body of water in order to resist the downward hydraulic pressure. Therefore the bottom of the body of water must be accessible, which either limits the depth of water in which the Ono system can be used or requires additional, expensive equipment to position and maintain the system.
U.S. Pat. No. 4,104,006 issued to Meiri discloses a wind-powered energy conversion device. The device includes a pair of flaps which are connected to the piston of a piston-cylinder type pump by cable. A tension spring is connected between the piston and the platform upon which the piston pump is mounted. As wind lifts the flaps the cable pulls the piston upwardly and stretches the spring. When the wind decreases the spring pulls the piston back down. The Meiri device does not use or require a float and is rigidly mounted to the platform or ground.
A drawback to the prior wave energy extraction devices is that they are relatively complex and expensive to maintain and manufacture. Since one of the main purposes of developing wave energy extraction devices is to reduce the cost of energy, the costs involved in maintaining and the manufacturing the wave energy extraction devices is a very important factor in the practicability of the devices. Thus, there is a need in the art for a wave energy extraction device which is inexpensive to manufacture and maintain.